1. Technical Field of the Invention
The present invention relates to controllers, disk drives, and related methods.
2. Description of Related Art
As is known, many varieties of disk drives, such as magnetic disk drives, are used to provide data storage for a host device, either directly, or through a network such as a storage area network (SAN) or network attached storage (NAS). Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disks (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices provide high storage capacity in a cost effective manner.
Disk drives include one or more drive devices, such as the spindle motor that spins the disk at a substantially constant velocity, and the actuator that positions one or more read/write heads over the surface of the disk. The demand for increased spin rates, higher recording and storage densities, and faster access times provides challenges for these corresponding controllers to provide fast and accurate control of these respective drive devices. Moreover, when the disk is mounted or potentially shifted in the drive, any resultant offset in the disk from its original relative center additionally will result in sinusoidal harmonic disturbances in the measured track position. Prior art controllers have attempted to compensate for these sinusoidal variations by calculating, for instance, a control effort based upon sinusoidal and cosinusoidal look-up table values on a wedge-by-wedge basis. This requires, among others, both the time to process and retrieve these wedge-dependent values, and the space to accommodate and store a large enough table to provide accurate and precise real-time control. Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present invention.